1. Field of the Invention
The present invention relates to an airbag inflator and a gas generator for airbag apparatuses for alleviating impacts on passengers at time of collision of vehicles, and more specifically to an airbag inflator, in which the interior of its housing is divided into two or more chambers by a partition wall joined by friction welding.
2. Prior Art
A conventional airbag inflator has, accommodated in its housing, with a gas discharge port(s), an ignition means actuated and ignited when a vehicle receives an impact, and a gas generating means that generates a gas when the ignition means is activated. Generally, a diffuser shell, having the gas discharge ports, and a closure shell, closing the diffuser shell together, form the housing of the airbag inflator. The diffuser shell and the closure shell are joined by a variety of welding methods, such as plasma welding, friction welding, projection welding, electron beam welding, laser welding and TIG (tungsten inert gas) welding. When the housing, whose interior is divided into two or more chambers by a partition wall, is used to form the airbag inflator, in particular, the friction welding is the most desired of the above welding methods because it can join the diffuser shell and the closure shell of the housing as well as the partition walls in a single operation.
The friction welding melts the members to be joined by friction heat to weld and join them, and thus an excess part of the melted material usually flows out, forming projecting weld burrs at the welded portion. In designing the housing, therefore, a space needs to be secured in the housing beforehand to accommodate the projecting weld burrs. In the airbag inflator whose partition walls defining chambers in the housing are joined by friction welding, a space that is not necessary for the operation of the airbag inflator must be provided for the protruding weld burrs. The protruding weld burrs constitute an obstacle in the way of reducing the size of the airbag inflator.
This space, unnecessary for the functioning of the airbag inflator, may be reduced by removing, where possible, the protruding weld burrs formed by the friction welding. The weld burrs, even if scraped off, may remain in the housing and interfere with the normal operation of the airbag inflator. To remove the weld burrs requires an additional process, reducing the efficiency in the manufacture of the airbag inflator.
The conventional airbag inflators are classified into two groups, i.e., electrical ignition type and a mechanical ignition type. The electrical ignition type airbag inflator uses heat produced by electric current to trigger an igniter to ignite a transfer charge, whereas the mechanical ignition type airbag inflator uses a plunger launched from a mechanical sensor to pierce and activate a detonator and thereby burn the transfer charge. Of these, the mechanical ignition type airbag inflator has the advantage of not requiring electric wiring and of low cost.
The mechanical ignition type airbag inflator generally accommodates ignition means, a gas generating agent, and a coolant/filter provided in the housing having gas discharge ports. The ignition means includes a mechanical sensor that launches a plunger upon detecting an impact by mechanical means; a detonator that fires when pierced by the plunger; and a transfer charge ignited by the flame of the detonator and burns the gas generating agent. The gas generating agent, when ignited and burned by the flame of the transfer charge, generates a gas, which is cooled and purified by the coolant/filter. In order to shoot the plunger from the mechanical sensor such that it precisely pierces the detonator, a correct positional and directional relationship must be established between the mechanical sensor and the detonator. Hence, the conventional mechanical ignition type airbag inflator requires the positioning of the mechanical sensor and the detonator, and this positioning process is an obstacle to the efficient manufacture of the airbag inflator.
It is, therefore an object of this invention to provide an airbag inflator which can solve the problems experienced in the conventional airbag inflators and can obviate the need for the space in the housing for weld burrs formed by friction welding and also the need for the process of removing the weld burrs, thereby reducing the overall size of the airbag inflator and preventing the airbag inflator from being affected by the removed weld burrs. It is also an object of this invention to provide an airbag inflator that can effectively utilize the protruding weld burrs.
The airbag inflator of this invention is characterized in that the shape of the projecting weld burrs formed on the partition wall on the side of an ignition means accommodating chamber, which is defined inside of the partition wall, is controlled by the weld burr restriction member during the friction welding.
More specifically, the airbag inflator of this invention comprising a housing having gas discharge ports and partition walls, joined by friction welding, which divide the interior of the housing into two or more chambers, the inner defining an ignition means-accommodating chamber, is characterized in that the shape of protruding weld burrs formed by the friction welding on the side of the ignition means accommodating chamber is controlled by a weld burr restriction member such that a space to accommodate an ignition means can be provided.
The above airbag inflator may be either a mechanical ignition type airbag inflator that produces a gas upon detecting an impact exclusively by a mechanical means or an electrical ignition type airbag inflator that is actuated upon receiving an electrical signal transmitted from a sensor that detects an impact, as long as the interior of the housing with gas discharge ports is divided into two or more chambers by the partition walls that are joined together by friction welding and which define the ignition means accommodating chamber on the inner side thereof.
The mechanical ignition type airbag inflator has ignition means, a gas generating agent, and a coolant/filter all installed in the housing with gas discharge ports. The ignition means includes a mechanical sensor that launches a plunger upon detecting an impact; a detonator which, when pierced by the plunger, ignites and burns; and a transfer charge that is ignited and burned by the flame of the detonator. The gas generating agent is ignited and burned by the flame of the transfer charge. The coolant/filter cools and purifies the produced gas. The electrical ignition type airbag inflator, on the other hand, is installed within the housing, with gas discharge ports and ignition means, which includes an igniter triggered by an electrical signal transmitted from a sensor that has detected an impact and a transfer charge that is ignited and burned by activation of the igniter, a gas generating agent that is ignited and burned by the flame of the transfer charge to produce a gas, and a coolant/filter that cools and purifies the produced gas.
As to the control of the shape of the protruding weld burrs on the ignition means accommodating chamber side, the protruding weld burrs may be so shaped that it can position, and/or block rotation of, a member which constitutes the ignition means in the ignition means accommodating chamber and that is installed in a place where the weld burrs project. This applies to a case where the mechanical ignition type airbag inflator, particularly, the ignition means installed in the ignition means accommodating chamber, includes a mechanical sensor that launches a plunger upon detection of an impact, a detonator that fires when pierced by the plunger, and a transfer charge ignited by the flame of the detonator. If the member installed in a place, where the weld burrs project, is a mechanical sensor, the shape of the protruding weld burrs is controlled beforehand so that the detonator can reliably be pierced by the plunger of the sensor, without providing a separate means for positioning the sensor.
Such a rotation prevention and/or positioning means may be realized by forming a positioning portion on the outer circumferential surface of the member which is installed in a place where the weld burrs project; and by controlling through the weld burr restriction member the shape of the protruding weld burrs formed on the partition walls on the ignition means accommodating chamber side into a shape such that the positioning portion of the member to be installed in a place where the weld burrs project can be fitted in the protruding weld burrs. The engagement between the positioning portion and the weld burrs can be achieved by providing them with matching recesses and projections and then fitting them together, or by forming the positioning portion and the weld burrs into complementary polygonal shapes and then fitting them together.
The control of the shape of the protruding weld burrs formed on the ignition means accommodating chamber side of the partition walls may be achieved, for example, by inserting the weld burr restriction member into the ignition means accommodating chamber which define the ignition means accommodating chamber on its inner side while performing the friction welding of the partition walls and then, removing the weld bur restriction member after the friction welding is finished. The weld burr restriction member may be formed integrally with the friction welding table used in the process of friction-welding the housing.
The housing is formed by joining the diffuser shell having gas discharge ports and the closure shell having a sensor accommodating opening. This Joining is done by friction welding.
The gas generating agent can be known gas generating agents such as azide-containing agents and non-azide-based agents. The azide gas generating agents include inorganic azide that has been in wide use such as an equivalent compound of soda azide and copper oxide, particularly the one based on sodium azide. The non-azide gas generating agents include compounds having, as main components, an organic nitrogen compound, such as tetrazole, triazole and their metal salts, and an oxygen containing oxidizing agent such as alkali metal nitrate; and compounds which use triaminoguanidine nitrate, carbohydrazide and nitroguanidine as a fuel and nitrogen source and also nitrate, chlorate and perchlorate of alkali metal or alkaline earth metal as an oxidizing agent. In terms of safety, it is more advantageous to use a non-azide gas generating agent.
The coolant/filter has a function of removing combustion residues produced as a result of combustion of the gas generating agent and also cooling the combustion gas. The coolant/filter may be formed of annular laminated layers of wire mesh made of stainless steel, such as SUS304, SUS310S, and SUS316 (JIS Standard) being compression-molded. The coolant filter may also be a combination of the conventional filter and coolant that are in wide use.
In the airbag inflator of this invention, an impact triggers the ignition means to ignite the transfer charge, whose flames in turn ignite and burn the gas generating agent, which produces a gas. The generated gas is cooled and purified by the coolant/filter before being injected through the gas discharge ports of the housing into the airbag.
Further, the above airbag inflator may be combined with an airbag to be inflated by introducing a gas generated by the airbag inflator, and a module case containing the airbag to form an airbag apparatus. This airbag apparatus is installed and secured in an appropriate location in a vehicle, such as steering wheel and dashboard.